Sealing of condensers and similar apparatus



J. A. KATER March 26, 1940.

SEALING 0F CONDENSERS AND SIMILAR APPARATUS Filed Dec. 20, 1938 /FWMM/NVEN?"OR By J. A. KA 75/? RNE Y Patented Mar. 26, 1940 v UNITED STATESPATENT OFFICE SEALING F CONDENSERS AND SIMILAR APPARATUS Joseph A.Kater, Teaneek, N. 1., alaignor to Bell Telephone Laboratories,

Incorporawd, New

This invention relates in general to the sealingof electrical devicesand more particularly to the sealing of condensers or similar apparatusin a container to prevent the entrance of moisture l and to bring aboutsuch sealing without causing a change in the electrical characteristicsof the device.

In the manufacture of precision type mica condensers it has been apreferred practice to dip the assembled units in an asphaltic compoundand then pot them in the same compound in a suitable container. However,when the units are dipped in such a compound changes in capacity occurwhich are not accurately predictable and it therefore is necessary inmany cases to unpot the condenser units and adjust their capacity to thedesired value by varying the pressure on the clamping plates and thenrepot them. Since these operations take place after the final drying ofthe unit an opportunity is afforded for moisture to get into the unitand be sealed in, resulting in detrimental eflects on temperaturecoeilicient, conductance, and aging of the completed condenser.

It is an object of the present invention to produce an electricalcondenser which will have improved electrical characteristics such as alow conductance and a low temperature coeflicient and onein which thesecharacteristics will be maintained fora long life even when subjected toextreme temperature changes.

It is also an object of the present invention to make possible thesealing of electrical apparatus with compounds which have desirablecharacteristlcs as sealing material but which are detrimental toelectrical units if used as potting compounds in the usual sense. I 1

To accomplish this and other objects and in accordance with the featuresof this invention there is provided a construction in which theelectrical unit is so mounted and sealed that its elements are free toexpand and contract when subjected to. extreme changes in temperaturewithout permitting the entrance of any moisture 5 into the unit.

The invention may be more clearly understood by referring to theattached drawing in which the single figure is a cross-sectional viewshowing in elevation one embodiment of the invention. In

n this drawing there is disclosed a standard type dry stack condenserimit consisting of alternate sets of conducting plates 5 and 6 separatedand insulated from each other by means of mica sheets and clampedbetween clamping plate I u and a similar clamping plate which isprovided with threaded openings to receive the clamping screws 0. Theplates 5 are extended at one side of the clamping plates and areconnected to a terminal member 9 and the plates 6 are extended at theopposite side of the clamping plate and g are connected to a terminalmember III. This condenser unit is positioned in a cup-shaped metalliccontainer II which is open at one end and is preferably seamless formedby an extruding operation so that when the open end is per- 10 fectlysealed there is no possibility of the entrance of moisture within thecontainer. Before positioning the unit within the container the latteris provided with an insulating lining l2 of paper or similar material.

After the unit is in position the container is filled to the top of theclamping plate I with a layer of granulated insulating material It whichis packed by tapping the container during the filling process. For thispurpose dry sand 20 No. mesh and free from water soluble material hasbeen found satisfactory. The sand-filled condensers are preferablyheated under atmospheric pressure for a period of approximately sixteenhours at a temperature of 250 to 300 F. and for 25 approximately fivehours under an absolute pressure not exceeding one-half inch of mercury,the temperature being maintained at 250 to 350 1''.

Immediately after removing the condensers 30 from the drying tank alayer H of a high viscosity asphaltic compound is poured into thecontainer at a temperature of 350 to 400 F. and care is taken to insurethat it sovers the insulation and wets the terminals and containers in 5order not to leave any paths through which moisture or liquid maypenetrate to the sand. A composition which has been found satisfactoryfor this purpose comprises about 75 per cent asphalt and 25 per centrosin and rosin oil. This 40 compound has a high viscosity at thepouring temperature and does not penetrate into the body of sand.

After the condensers have cooled to room temperature a layer II ofmineral wax which has a melting point between 152 F. and 162 F. and issufiiciently fiuid to pour freely at a temperature 180 F. to 220 F. ispoured over the layer ll of asphaltic compound, the latter preventingthe mineral wax from penetrating into the underlyto lug body of sand andunit. At the temperatures stated this mineral wax is of low viscosityand bonds with the terminals, walls of the container and the underlyinglayer of asphaltic compound to form an efiicient seal which remainseffective at the lowest temperatures to which the apparatus may besubjected in service. A strip of insulating material i6 dimensioned toclosely fit the container is placed over the wax layer IS, the terminalmembers 9 and Ill passing through close-fitting openings in theinsulating strip which is preferably of Bakelite or similar material. Aclose-fitting cover I1 is then forced in place over the container II,this cover being provided with comparatively large perforations topermit the passage of terminals 9 and I0 therethrough. The cover llserves both to protect the device from injury and to retain the wax i5in position at operating temperatures at which there is a tendency forcold flow.

The body of sand or similar material surrounds the condenser unit on allsides but the bottom side and allows the unit to expand and contract inaccordance with temperature changes without otherwise materiallyaffecting the characteristics of the unit. Furthermore this body ofsand, because of the large surface area of its individual grains, isbelieved, to a certain extent, to function as a dessicant for anymoisture included within the unit or container while the method ofsealing prevents the entrance of moisture under the most severe serviceconditions. In certain types of apparatus it is required that condensersbe mounted on poles where they may be subjected to an extremetemperature range which may vary from as low as F. in the winter time toas high as 140 F. in the summer time with the sun shining directly onthe apparatus case. Condensers in accordance with this invention havebeen found to satisfactorily withstand such a range in temperature.Furthermore, accelerated life tests show that such condensers age onlyabout one-tenth as much as condensers potted in standard manners andtheir temperature coeflicient is on an average only about one-tenth asgreat.

While this method of sealing is particularly adaptable for sealingcondensers, it is obvious that it may be used to advantage inheremetically sealing other types of electrical apparatus such, forexample, as transformers, induction coils, etc.

What is claimed is:

1. An electrical device comprising a container open at one end, anelectrical unit positioned therein with terminals extending through theopen end of said container, a body of dry granular insulating materialsurrounding and covering said unit, and a dual compound seal, fillingthe open end of said container and consisting of an outer soft compoundand inner hard compound for preventing the entrance of moisture to saidunit.

2. An electrical device comprising a container open at one end, anelectrical unit positioned therein with terminals extending through theopen end of said container, means for sealing the open end of saidcontainer comprising a soft sealing compound for preventing the entranceof moisture to said unit, a hard compound for preventing the entrance ofsaid soft compound to said unit, and a body of a granular insulatingmaterial surrounding said unit for preventing the entrance of said hardcompound to said unit.

3. An electrical device comprising a container open at one end, anelectrical unit positioned therein with terminals extending through theopen end, a body of granular insulating material surrounding said unitand a plurality of layers of viscous insulating materials for preventingthe entrance of moisture to said unit and mixing of said materials, saidlayers of materials having progressively higher softening temperaturesfrom the open end of said container inward.

4. An electrical device comprising a container open at one end, anelectrical unit positioned therein, a body of granular insulatingmaterial surrounding and covering said unit, a layer of asphalticcompound covering said granular material, a. layer of mineral waxcovering said compound, and means for retaining said wax within saidcontainer.

5. An electrical device comprising a container open at one end, anelectrical unit positioned therein, a body of sand surrounding andcovering said unit, a layer of asphaltic compound covering said body ofsand, a layer of mineral wax covering said compound, and means forretaining said wax in said container.

6. An electrical device comprising an extruded metallic container openat one end, an electrical unit positioned therein, a body of sandsurrounding and covering said unit, a layer of an asphaltic compoundhaving high viscosity at pouring temperatures covering said sand, alayer of mineral wax having low viscosity at pouring temperaturescovering said compound, and means for retaining said wax within saidcontainer.

7. An electrical condenser comprising an extruded metallic containeropen at one end, a condenser unit positioned therein, a body of sandsurrounding and covering said unit, a layer of asphaltic compound havinghigh viscosity at a pouring temperature of 350 to 400 F., a layer ofmineral wax having low viscosity at a pouring temperature of 180 to 220F., and means for retaining said wax within said container.

8. An electrical condenser comprising a condenser unit, a containertherefor having an opening at one end, granulated material which doesnot adhere to said unit or said container and which is infusible below400 F. for embodying said unit in said container, an insulatingsubstance which does not crack at low service temperatures for sealingthe open end of said unit and a compound having a relatively highmelting point between said substance and said material.

9. An electrical condenser comprising a container having an opening atone end, a condenser unit embedded in sand in said container, a terminallead electrically connected to said unit and passing through saidopening, a mineral wax having a melting point between 152 and 162 F. forsealing the open end of said container and a layer of compoundcomprising asphalt and rosin between said sand and said mineral wax.

10. The method of hermetically sealing an electrical device within acontainer open only at one end which consists in positioning said devicewithin the container, pouring sufficient sand in said container tosubstantially cover said unit, covering said body of sand with a layerof asphaltic compound which is highly viscous at pouring temperatures,allowing said compound to cool and then pouring thereon a layer ofmineral wax which is of low viscosity at pouring temperatures.

11. A method of sealing an electrical condenser unit within a containeropen at only one end which consists in positioning said unit within thecontainer, substantially surrounding said unit with sand, heating at atemperature of 250 to 300 F. under atmospheric temperature, furtherheating at said temperature range under an a mmmmfi Mm m; m M im mmmmmmmwmm J A mu m mmm m mmm wmmfimmmmm Ja mm mmm m Fm m mmmm mmmmmmmmmm mm

